In order to achieve a high-performance speed regulation of a permanent magnet synchronous motor, a resolver is required to accurately detect the position of a rotor of the permanent magnet synchronous motor. The accuracy of the detected position of the rotor of the permanent magnet synchronous motor is important for the performance of a motor control system, a fail of which may even cause an unstable operation of the motor speed regulation system. For convenient use in practices, in the installation of the resolver, it is required to ensure that an initial zero position of the motor is consistent with an initial zero position of the resolver, which is however difficult due to many factors.
The electrical principle of a brushless resolver is shown in FIG. 1. A primary excitation winding (R1-R2) of the resolver and orthogonal secondary induction windings (S1-S3, S2-S4) of the resolver are all located on a stator side. As shown in FIG. 1, no winding is arranged on the rotor of the variable reluctance resolver. Because of the special design of the rotor, a secondary coupling varies sinusoidally as an angle position varies. In a case where the rotor of the resolver rotates with the motor synchronously and an alternating-current excitation voltage is applied to the primary excitation winding, inductive potentials are generated in the two secondary output windings, with values of a product of a sine value of a rotation angle of the rotor and the excitation and a product of a cosine value of the rotation angle of the rotor and the excitation. Therefore, a rotor angle can be measured with the resolver. The input and outputs of the resolver have a relation as:
                    {                                                                                                  E                                                                  R                        ⁢                                                                                                  ⁢                        1                                            -                                              R                        ⁢                                                                                                  ⁢                        2                                                                              =                                                            E                      0                                        ⁢                    sin                    ⁢                                                                                  ⁢                    ω                    ⁢                                                                                  ⁢                    t                                                                                                                                            E                                                                  S                        ⁢                                                                                                  ⁢                        1                                            -                                              S                        ⁢                                                                                                  ⁢                        3                                                                              =                                                            KE                                                                        R                          ⁢                                                                                                          ⁢                          1                                                -                                                  R                          ⁢                                                                                                          ⁢                          2                                                                                      ⁢                    sin                    ⁢                                                                                  ⁢                    θ                                                                                                                                            E                                                                  S                        ⁢                                                                                                  ⁢                        2                                            -                                              S                        ⁢                                                                                                  ⁢                        4                                                                              =                                                            KE                                                                        R                          ⁢                                                                                                          ⁢                          1                                                -                                                  R                          ⁢                                                                                                          ⁢                          2                                                                                      ⁢                    cos                    ⁢                                                                                  ⁢                    θ                                                                                ,                                    (        1        )            where E0 represents a maximum amplitude value of excitation, ω represents an excitation angular frequency, K represents a ratio of the resolver, and θ represents an axial angle by which the rotor rotates.
When a direct current is applied to a stator winding of the motor, a constant magnetic field is generated on the axis of the winding. Ideally, the constant magnetic field and the magnetic field of the permanent magnet rotor attract the rotor to a same position. In this case, an initial zero position of the permanent magnet rotor can be detected with the above method.
FIG. 2 is a schematic diagram of an initial positioning of a permanent magnet synchronous motor according to a conventional technology. As shown in FIG. 2, in an initial positioning of a resolver, generally, a direct current inflows from phase A (A1-A2), and outflows from phases B (B1-B2) and C (C1-C2). In this case a direction of a resultant magnetic field is an axis direction of phase A, i.e., a direction vertical to a horizontal line (defined as a zero position of the motor). Ideally, a constant stator magnetic field and a magnetic field of a permanent magnet rotor may attract the rotor to a same position, that is, the rotor of the motor is driven to and locked at the zero position of the motor, thereby correcting a deviation between the zero position of the resolver and the zero position of the motor. However, a friction resistance and a cogging torque always exist in the permanent magnet synchronous motor even if the motor is in an unloaded state. Therefore, in the initial positioning of the resolver, the rotor of the motor cannot be completely driven to and locked at the axis direction of phase A (i.e., the zero position of the motor), and thus an error angle Δθ exists in an initial orientation of the magnetic field of the rotor of the motor.
As can be seen, it is desired to solve by those skilled in the art the problem of how to correct the initial zero position deviation between permanent magnet synchronous motor and resolver.